The stabbing came as a trial was underway in the capital for alleged accomplices of the authors of the January 2015 attack on the Charlie Hebdo weekly that claimed 12 lives.
A police operation is ongoing in northeastern district of Paris, with local authorities asking people to avoid the area.
Several schools in the sector have been closed with staff and pupils inside as precautionary measure. Parents have been told to stay away for now.
Paris deputy mayor Emmanuel Gregoire also said on Twitter that police was looking for a "potentially dangerous" individual.
Jean Castex, the French Prime Minister, is reportedly heading to the 'Crisis Room' at the Interior Ministry to follow developments, cutting short a trip to a suburb north of Paris.
The attack comes in the wake of multiple death threats made against Charlie Hebdo employees. The head of Human Resources said earlier this week she was given "10 minutes" to leave her home after police received credible death threats.
This is a breaking news story. More to follow.
Four people were injured, two seriously, in a knife attack in Paris Friday near the former offices of French satirical magazine Charlie Hebdo, a source close to the investigation told AFP.
At least two of the victims were in a critical condition with life-threatening injuries, the Paris police department said. One suspect has been arrested near the Bastille plaza in eastern Paris, according to police.
A security cordon has been erected around the former offices of Charlie Hebdo and bomb disposal experts have been called in following the discovery of a package.